The present invention relates generally to systems and methods for analyzing the quality of a weld. More specifically, the present invention relates to systems and methods for analyzing a weld image to determine the quality of the weld.
Resistance welding techniques are used in many manufacturing processes, such as the automotive industry. Resistance welding techniques include spot, seam and projection welding. The exemplary embodiments of the present invention disclosed herein are particularly useful for spot welds, but may find applications in other resistance welding techniques and other manufacturing processes.
In spot welding, a nugget of weld metal is produced between two base metals at an electrode site. A coordinated application of electric current and mechanical pressure of the proper magnitudes and durations is needed to assure a suitable nugget is formed. For example, the current density and pressure must be high enough to form a nugget, but not so high that molten metal is expelled from the electrode site. Also, the duration of weld current must be sufficiently short to prevent excessive heating of the electrode faces.
Surface marking results from base metal shrinkage, caused by a combination of the heat of welding and electrode penetration into the surface of the base metal. The surface mark includes a circular ridge around a spot weld concavity centered around the nugget. The diameter of the nugget (called the xe2x80x9cinner diameterxe2x80x9d of the spot weld) must meet the requirements of the appropriate specifications or design criteria. For example, one specification requires that spot welds have a minimum nugget diameter of 3.5 to 4 times the thickness of the thinner base metal sheet.
One problem lies in estimating the inner diameter of the spot weld without pulling apart or otherwise destroying the weld. In the past, visual inspection by a human inspector has been used. However, this type of testing is inherently subjective, inconsistent, and labor-intensive. Ultrasonic inspection has also been implemented. However, this type of testing requires carefully applying an ultrasonic sensor to the weld, which requires time and precision. Ultrasonic inspection also requires complex signal analysis. Other types of testing include the hammer and chisel method, and detachment of the spot weld from the base metals. However, these two tests are destructive tests, and can only be performed on a few random samples.
Accordingly, there is a need for an improved system and method for determining the inner diameter of a spot weld to determine the quality of the weld. Further, there is a need for an improved system and method for non-destructively analyzing a weld. Further still, there is a need for a system and method for analyzing the quality of a plurality of welds quickly and efficiently in a manufacturing environment. Further yet, there is a need for a system and method for analyzing the quality of a weld which does not require determination of the center of the weld on the metal sheet prior to performing the analysis.
According to one exemplary embodiment, a method of determining a measure of the quality of a spot weld based on a set of image data representing an image of the spot weld includes identifying the image data into a first data set and a second data set, the first data set taken to be weld data and the second data set taken to be background data, and estimating an inner diameter of the spot weld based on the weld data. The image data includes weld data and background data. The estimation provides a measure of the quality of the weld.
According to another exemplary embodiment, a system for determining the quality of a weld includes a video camera and a computer program. The video camera is configured to acquire a set of image data representing an image of the weld. The computer program is embodied on a computer-readable medium and is configured to receive the image data, identify weld data in the image data, and estimate a diameter of the weld based on the weld data. The diameter of the weld indicates the quality of the weld.
According to yet another exemplary embodiment, a computer program for analyzing a set of image data representing an image of a weld includes means for separating the weld data from the background data and means for calculating the surface brightness of the spot weld based on the weld data. The image data includes weld data and background data. The surface brightness indicates the quality of the weld.